1. Field of the Invention
The present invention relates to a key switch and a keyboard provided with a plurality of key switches.
In order to improve portability of a portable apparatus, such as a notebook-type personal computer, provided with a keyboard, it is required to reduce thickness of the apparatus. Accordingly, it is required to reduce height of the keyboard which is built in the portable apparatus.
For operability of a key switch of such a keyboard, it is required that a key top moves smoothly, a stroke of the key top is greater than a predetermined distance and wobbliness of the key top is at its minimum. The wobbliness of the key top affects operability of key-stroking if the fingertip of the user presses a position near periphery of the key top. In such a case, the key top will be inclined and will be pressed down in an inclined state. The user then feels that the operability of the keyboard is not good.
2. Description of the Related Art
An exemplary key switch of the related art includes a key top, a housing and a dome-shaped rubber spring member. The key top includes a cylindrical part at its lower surface. The cylindrical part is fitted to a guide cylinder provided on the housing. The dome-shaped rubber spring member is mounted on the housing and presses up the key top. The key top moves vertically while being guided by the guide cylinder. It is difficult to reduce the height of such a key switch since the cylindrical part and the guide cylinder must be provided.
As an improved version of such a key switch, a key switch is known which includes a key top, a housing, an X-shaped link mechanism and a spring member. The link mechanism includes two linking members assembled in an X-shape. The link mechanism is provided on the housing. The key top is provided on an upper side of the link mechanism. The key top is supported by the link mechanism and moves in a vertical direction.
The key switch provided with such a link mechanism eliminates the need for a guiding mechanism for vertical movement of the key top since the link mechanism supports the key top. Therefore, the height of the key switch provided with link mechanism is reduced compared to the height of the key switch provided with the cylindrical part and the guide cylinder. However, further reduction of the height of the key switch is desired.
The notebook type personal computer is carried in such a state that a liquid crystal panel is folded against the keyboard. In order to improve portability, it is required to reduce the thickness of the notebook type personal computer in the folded state. Accordingly, the height of the key switch needs to be reduced only in a state where the liquid display panel is folded against the keyboard.
Based on this concept, the applicant has proposed an improved key switch having such a link mechanism in Japanese Patent Application No. 11-347887 titled xe2x80x9cKey switch and a key board.xe2x80x9d This key switch is configured such that the key top is depressed when it is not in use.
FIG. 1 is an exploded diagram showing a key switch 10 of the related art. The key switch 10 includes a key top 20, an X-shaped link mechanism 30, a fixed base 40, a movable plate 50, a membrane switch sheet 60 and a supporting plate 70. The link mechanism 30 includes a first link 31 and second link 32 which are assembled in a crossed configuration. The first link 31 is provided with a leaf spring 33 fixed thereon. The link mechanism 30 is supported on the fixed base 40 and the key top 20 is held horizontally with four bearing parts 21 formed on its back surface being fitted with shaft parts at upper ends of the first and second links 31 and 32. The leaf spring 33 touches a lug part 51 of the movable plate 50. When the key top is pressed, for example by a fingertip, the first and second links 31 and 32 of the link mechanism 30 are pivoted to incline and the leaf spring member is flexed. When the fingertip is released from the key top 20, the first and second links 31 and 32 are pivoted to rise by a spring force of the leaf spring member 33. Thus, the key top 20 is lifted and moves back to its initial position.
When the movable plate 50 is moved in a Y1-direction, the first and second links 31 and 32 of the link mechanism 30 is pivoted to incline. The key top 20 moves downwards until it abuts the fixed base 40. This may be referred to as a depressed state of the key top. Thus, the key top 20 now has a reduced height.
However, since the first and second links 31 and 32 of the link mechanism 30 needs to be accommodated within a region defined by a projection of the key top 20 on the fixed base 40, the four shaft parts at the tip of the first and second links 31 and 32 are provided at proximate position to each other when in a raised position. Thus, the four parts supported by the four shafts at the tip of the first and second links 31 and 32 of the key top 20 are placed within a region near the central part of the key top 20. Accordingly, the key top 20 is supported at the portion near its center and thus is in a wobbly state.
Accordingly, it is a general object of the present invention to provide key switch and a key board having such key switches.
It is another and more specific object of the present invention to provide key switch and a key board having such key switches which can reduce the problems described above.
In order to solve the problems described above, a key switch is provided, which includes:
a switch provided on a base;
a key top for operating the switch;
a link mechanism supported on the base and supporting the key top on its upper side, a shape of the link mechanism being changed when the key top is depressed;
a movable plate provided on the base such that the movable plate is moved when the key top is depressed so as to change the shape of the link mechanism to the flat shape; and
an auxiliary link mechanism having a first side part supported by the base and a second side part supporting the key top.
With the above-described key switch having an auxiliary link mechanism, wobbliness of the key top is reduced and thus feel of operation of a key-stroking operation can be improved. Also, since the link mechanism can change its shape to a flattened shape by moving the movable plate, the key top may be take its lowered position while the keyboard is not in use.